1. Field of the Invention
The field of the invention is data processing, or, more specifically, methods, apparatus, and products for sharing kernel services among kernels.
2. Description of Related Art
A thread is a unit of software execution on a multi-threaded computer. That is, a thread is an executable entity of work in a computer system. A thread can be viewed of as a separate stream of executable computer program instructions. On such a computer, software programs are executed in units of execution called ‘processes’ that include all the processor registers, code segment and offset registers, data segment and offset registers, stack segment and offset registers, flag registers, instruction pointer registers, program counters, and so on, needed for execution of software programs. For efficiency, ‘processes’ are organized further as threads, where each thread of a process individually possesses all the attributes needed for execution except that a thread shares memory among all the other threads of a process, thereby reducing the overhead of operating system switches from thread to thread (‘context switches’).
Two modes of multi-threading are discussed in this specification: simultaneous multi-threading (‘SMT’) and single-threaded (‘ST’) multi-threading. ST multi-threading is time-multiplexed multi-threading, that is, multi-threading by use of time slices or time quanta. In ST mode, both individual threads and virtual processors are assigned to a portion of a processor's computing capacity apportioned in segments of time, each of which is referred to as a ‘time slice’ or ‘time quantum.’
Some processors accept computer program instructions from more than one thread simultaneously, a feature referred to as ‘simultaneous multi-threading’ or ‘SMT.’ The idea behind SMT is to share the processor hardware on a chip among multiple threads of a multi-threaded workload. SMT is a technique that lets multiple independent threads issue instructions to a single physical processor in a single processing cycle. Traditional processor architectures issue instructions to a processor from only one thread at a time. An example of a processor that implements SMT as described here is IBM's Power5™ processor.
SMT is implemented on physical processors each of which is capable of accepting instructions from more than one thread of execution simultaneously. Also in SMT mode, both virtual processors and threads running on virtual processors may be apportioned through time slices. A thread of execution on a virtual processor in SMT mode may be viewed as running on a logical processor. A virtual processor running on a physical processor in SMT mode therefore may be viewed as supporting more than one logical processor. Whether a thread runs in ST mode or in SMT mode, a thread running on a logical processor is unaware of the logical or virtual nature of the processor and views it as a traditional processor.
Multiprocessing is implemented in computers that support multiple logical partitions in ST mode or SMT mode partition-by-partition. Each partition traditionally implements an entire separate operating system including a separate kernel. Kernels support applications running in logical partitions by providing kernel services. Although the types of services provided by kernels are generally similar, different kernels may implement services in different ways. For this reason, some kernels may be better than other kernels at providing certain kernel services. In traditional art, however, a kernel having a superior service cannot share such a service with another kernel—not even with another kernel of the same type. An instance of a Unix kernel, for example, with a superior disk i/o driver traditionally could not make its disk i/o driver available to threads of execution running against another Unix kernel even if the other Unix kernel were of exactly the same type and version.